The broad, long-term objectives of this work are to establish a practical and empirically-sound means to assess children's acute stress reactions after potentially traumatic events (eg, accidents, fires, disasters) and to expand our understanding of acute traumatic stress responses in children. Brief, accessible measures of acute stress can optimize use of scarce mental health resources by identifying trauma-exposed children with immediate distress that warrants intervention and guiding efforts to prevent long-term sequelae. This study builds on an NIH-funded project that developed the first brief self-report measure for acute stress disorder (ASD) in children and adolescents (the Acute Stress Checklist for Children, or ASC-Kids), and subsequent work that utilized best practices in instrument translation / adaptation to create a Spanish version (the Reacciones Agudas Postraumaticas - Menores, or RAP-M). Specific aims of the current study are to assess the reliability and validity of the ASC-Kids and RAP-M in parallel samples of English- and Spanish-speaking children (200 each), to examine and compare the factor structures of the measures, and to assess potential differential item functioning between language versions. To achieve these aims, children (8 to 17) exposed to a potentially traumatic event within the past month will be recruited in healthcare settings in three states (PA, CA, FL) for an initial assessment and two brief follow-ups (1-7 days and 3 months later). The study will evaluate the measures'test-retest reliability, concurrent validity with clinician ASD diagnosis, convergent / discriminant validity (anxiety / depression symptoms), and predictive validity (later PTSD symptoms). Confirmatory factor analyses will assess the fit of three models, derived from theory and empirical literature, for the structure of ASD symptoms. Measurement invariance between English and Spanish versions will be examined via multi-sample CFA and by IRT analyses of differential item functioning. Associations between measures will also be examined in a bilingual sub-sample. This project addresses a key gap in assessment of child mental health consequences of trauma and violence and in assessment of Spanish-speaking children. It will advance the NIH objective of increasing mental health screening in health care settings, especially appropriate in the area of child acute stress because medical providers are among the first to see children after traumatic events such as traffic crashes, fires, or disasters.